Method of improving steel rails.



ROBERT ABBOTT HADFIELD, OF SHEFFIELD, ENGLAND.

, METHOD OF IMPROVING STEEL RAILS.

Specification of Letters Patent.

Application filed July 12. 1907. Serial No. 383.421.

Patented Feb. 18, 1908.

To all whom may concern-.- I

Be it known that I, ROBERT ABBOTT HAD-' FIELD, a subject of the Kingof-Great Britain residing at Sheflield, York county, England,

have invented a new and useful Method of Improvin Steel Rails, of whichthe following is a ,clear, and exact description.

The purpose of my invention is to improve the uality ofsteel railwayrails. The severity 0 the work put upon such rails by reason of theincrease in the weight of the cars and locomotives, and the speed of thetrains, has "been such, of recent years, as to cause a very largepercentage of rails to be broken in service. Rails made of steel whichrespond well to the ordinary tests for tensile strength, &c.,havebeenfound to be subject to fracture, by reason of brittleness and lackof resistance to shock; and although many attempts have been made toovercome this difficulty, all of these have failed, so far as I know, tofulfil the re uirements, either because of the undue cost 0 theexpedients which have been proposed, or because of their inefiiciency.

I have discovered that a very great improvement can be effected in thecapacity of the rails to resist shock, coupled with an increasedhardness of the rails, by a special heat treatment to which the railsare sub- -jected after they are manufactured. These two qualities ofresistance to shock and increased hardness have not ordinarily been.

regarded as possible to secure by any single treatment, for the increaseof hardness has heretofore been considered to result in increasedbrittleness. Careful tests have, however, showed that this is not thecase with rails treated by my invention.

My invention also enables excellent results to be obtained withoutreference to the phosphorous contents of the steel, which may varywithin certain limits. For example, I have found that steelcontainingu12 per cent. of phosphorus which is more than the Bessemerlimit of phosphorus; .44 per cent. carbon and .84per cent. of manganese,when treated by my invention, had a remarkably hard surfacecombinedwitha very good resistance to fracture when nicked and subjectedto drop test. Phosphorus, therefore, when the rail is subjected to mytreatment has the useful property of hardening in the manner in whichvanadium is supposed to act upon steel.

In order that those sln'lled in the art may be able to practice myinvention, I now describe it in what I regard its preferableperformance, premising that the details of the operation may be varied.

I take a steelrail to be treated, and having heated it, to a temperatureof at least 850 (1, I cool it, preferably by quenching, this quenchingbeing done either by subjecting the rail to thequick cooling action of aliquid, or by cooling it quickly in air. I then take the rail which hasbeen thus quenched and after it is at atmospheric temperature or whileit still retains some of the temperature imparted by the originalheating, anneal it by reheating to a lower temperature between 500 C.and 730 (3., preferably about 700 C. or instead ofthese two operationsof successive heating and quenching and then reheating to a lowertemperature, I may quench the heated steel so as'to cool it quickly downto a certain point, say about 700 (1, and then cool it slowly from thispoint downward, thus accomplishing in a single continuous operation whatis otherwise accom lished by two successive operations; as analternative, the rail in its heated condition as it leaves the rolls andwhile at the'requisite high temperature, may be guided into a tank anduenched or otherwise quickly cooled. It is t ien reheated, being, ifdesired, straightened lower temperature asmay be desired in order togive the requisite toughness or hardness. This final cooling may, ifdesired, take place on the rail-bed near other hbt rails so as to effectslow cooling. In connection with the initial heating to at least 850 C.and the second heating to between 500 and 700 (1, I wish to explain thatthese temperatures are not absolute but can be, of course, variedsomewhat, the essential object being to obtain such an initialrelatively high heat followed by such a relatively low heat as willultimately result in increased hardness and resistance to shock. of therail which has been treated. I may also, in order to prevent warping ofthe rail during the cooling, cool the parts of the rail differentially,applying a quicker cooling to the head, which contains a greater mass,than to the flange, where the mass is less and the loss of heat corres0ndingly reater in proportion. I pre er to effect t e heating of therail by immersing it in a molten bath of metal or of a fusible salt suchas barium chloridwhich may be maintained at a constant temperature bythe action of an electric curren The following is a statement of someresults which I have obtained by a treatment of steel in this manner:Steel containing ,38 carbon, .13 silicon, .06 phosphorus and .92manganese, and having an elastic limit of 29, tensile strength of 46,elongation of 23 and reduction of area of 43, when submitted, to a droptest to determine its brittleness or re sistance to shock, and a balltest to determine its hardness, gave the following results: Nicked andsubjected to drop test, '2 kilogrannneters X 3 degrees bending angle;without nick, similar test, 29X 70. Ball test for hardness, 193. The.same specimen, when heated to 970 C. and quenched in water, and thenreheated to 730 C. and cooled slowly in a furnace, had the followingproperties: Elastic limit, 30 tensile strength, 46; elongation, 26;reduction of area, 50. When nicked and subjected to drop test, 4-1/2kilogrammeters X 13 degrees bending angle. Subjected to ball test, 236.Another specimen having carbon .2, phosphorus .14 and manganese .86 had,when untreated, an elastic limit of 29; tensile strength of 46;elongation of25, and reduction of area of 37; and when nicked andsubjected to a drop test it gave 4-1 2 X 16 and under the ball test forhardness gave 166.

The same specimen when quenched in water.

at 960 C., reheated to 730 C. and cooled in a furnace, had an elasticlimit of 34; tensile strength of 42; elongation of 27, and reduc-.

tion of area of 51; and when nicked and subjected to drop test, gave7-1/2' X 23, and under the ball test, 187.

The advantages of my invention will be appreciated by those skilled inthe art, since it effectually overcomes the difficulties whichmanufacturers of steel rails have met, and provides a rail which,without undue increase of cost, is very greatly improved in respect ofits durability and resistance to shock.

My invention produces a rail having a tough matrix stiffened by thetreatment above described to produce a material having high elasticlimit and greater hardness as indicated by resistance to drop test.

I claim as my'invention:

1. The method herein described of treatin steel rails, which consists inheating the rail to a relatively high temperature, quickly cooling it,reheating it to a predetermined lower temperature than the initialheating,

and then subjecting it to a slower cooling, the

two heats being to predetermined degrees such as to concurrently produce*increased hardness and resistance to shock, substan-' tially asdescribed.

2. The'method herein described of treatin steel rails, which consistsin' heating the rai substantially as described.

to a temperature of at least 850 (3., quickly cooling it, reheating tobetween 500 and 700 0., and then subjecting it to a slower cooling 3.The method herein described of treating steel rails, which includes thesteps of heating the rail, quickly cooling from a redetermined hightemperature and a terwards slowly cooling from a predetermined lowertemperature, the two temperatures being such as to produce concurrenthardness of the rail and resistance to shock, substantially asdescribed.

- 1. The method herein described of treating steel rails, which includesthe steps of heating the rail, quickly cooling the rail from atemerature of at least 850 C. to a temperature etween 500 and 700 (3.,and afterwards slowly cooling the rail from a temperature of between 500to 700 (1., substantially as described.

5. The method herein described of treating steel rails containing morethan .1 per cent. of phosphorus which includes the steps of heating therail, quickly cooling it from a predetermined high temperature to apredeterminedlower temperature, and afterwards subjecting it to a slowercooling from said predetermined low temperature, the twosteel rails,which consists in heating the rai to a predetermined high temperature byimmersing it in a hot bath, quenching it to a predetermined lowtemperature, and afterwards subjecting it to a slower cooling from saidpredetermined lower temperature, the

two temperatures being such as to produce concurrently increasedhardness and resistance to shock, substantially as described.

7. The method herein described of treating steel rails containing morethan .1 per cent. of phosphorus, which includes the'steps of heating therail, quickly cooling from a predetermined high temperature, andafterwards slowly coollng from a predetermined lower temperature, .thetwo temperatures beingsuch as to produce concurrent hard-..

ness of the rail and resistance ,to shock, substantially as described.

. l v In testimony whereof, I have hereunto set my hand.

ROBERT ABBOTT HADFIELD.

